1. Field of the Invention
The present invention relates to a liquid crystal display device and a radio reception apparatus provided with the same.
2. Description of the Related Art
Hitherto two types of liquid crystal displays have been employed in liquid crystal display devices, which are the segment display type for displaying relatively simple data such as preset characters and numerals, and the dot matrix display type for displaying relatively complex characters and symbols by turning on and off the intersecting points of X- and Y-axes as dots. The segment display is driven by applying a low drive voltage, so that the duty ratio is low as well. By contrast, the dot matrix display involves a rather high duty ratio as well as a high drive voltage.
A variety of reception apparatuses have been developed which are capable of receiving signals in frequency modulation (FM) multiplex broadcasting which transmits character information by exploiting the remaining frequencies other than the transmission frequencies dedicated to audio information in FM broadcasting. One of those radio reception apparatuses which can receive FM multiplex broadcasting is such an apparatus comprising a liquid crystal display device of dot matrix display type as a display for displaying character information received in FM multiplex broadcasting.
However, in the conventional liquid crystal display devices, in which the drive voltage used for segment display and the drive voltage for dot matrix display are different from each other, when both segment display and dot matrix display are implemented with one and the same liquid crystal panel, the difference in drive voltage causes potential differences between electrodes which in turn cause positive and negative ions within the liquid crystals to adhere to the electrodes. As a result, a blackening/whitening phenomenon will occur, posing a problem of deteriorated display grade. For a solution of such a problem, if the drive voltage for the segment display is adjusted to the drive voltage for the dot matrix display, the display density in the segment display would be increased by a difference in duty ratio, resulting in a problem of an increased contrast difference between the segment display and the dot matrix display. To solve all these problems, it is necessary that the segment display and the dot matrix display be implemented by different liquid crystal panels correspondingly, or that a display section where the segment display is performed and a display section where the dot matrix display is performed are spaced to a large extent. In the former method, however, at least two liquid crystal panels would be involved so that the installation of liquid crystal panels would be restricted, in which case the equipment including these liquid crystal display devices would encounter problems in an equipment provided with such a liquid crystal device, such as deterioration in designability, upsizing and increase in failure rate. In the latter method, because of the need of using a larger liquid crystal panel and the occurrence of areas where the display is disabled in the liquid crystal panel, there would occur problems in an equipment provided with such as a liquid crystal display device, such as a deterioration in designability and upsizing.
In radio reception apparatus including the conventional liquid crystal display device, indeed character information received with a dot matrix display type liquid crystal display device during the reception of FM multiplex broadcasting, but the dot matrix display, if executed during the reception of amplitude modulation (AM) broadcasting, would be accompanied by generation of noise due to the voltage waveform of the drive voltage applied to the relevant display section. Moreover, since the fundamental waves of the frequency band of the noise are distributed over a wide range as broad as about 16 kHz to 48 kHz, and since a high drive voltage is involved, the resulting noise is so high that AM broadcasting using the frequency band of about 522 kHz to 1622 kHz would be greatly affected. Therefore, in this case, there is a problem that the dot matrix display cannot be executed while AM broadcasting is being received. Due to this, in the radio reception apparatus capable of receiving both FM multiplex broadcasting and AM broadcasting, the liquid crystal display device incorporated in the radio reception apparatus can be used only either during the reception of FM multiplex broadcasting or during the reception of FM broadcasting, such that effective use of the liquid crystal display device cannot be made. Actually, whereas frequency adjustment as well as recognition of the current broadcasting channel under reception can be readily accomplished by displaying the frequency band of current reception onto the liquid crystal display during the reception of FM multiplex broadcasting (FM broadcasting), the liquid crystal display cannot be used during the reception of AM broadcasting. Accordingly, a display section for adjustment needs to be provided independently, which would cause problems such as increase in size and deterioration in designability of an equipment provided with such a liquid crystal display device.